Description.
This lead acid battery charger circuit is designed in response to a request from Mr.Devdas .C. His requirement was a circuit to charge two 12V/7AH lead acid batteries in series.Anyway he did not mentioned the no of cells per each 12V battery. The no of cells/battery is also an important parameter and here I designed the circuit assuming each 12V battery containing 6 cells. When two batteries are connected in series, the voltage will add up and the current capacity remains same. So two 12V/7AH batteries connected in series can be considered as a 24V/7AH battery.

The circuit given here is a current limited lead acid battery charger built around the famous variable voltage regulator IC LM 317. The charging current depends on the value of resistor R2 and here it is set to be 700mA. Resistor R3 and POT R4 determines the charging voltage. Transformer T1 steps down the mains voltage and bridge D1 does the job of rectification. C1 is the filter capacitor. Diode D1 prevents the reverse flow of current from the battery when charger is switched OFF or when mains power is not available.

Circuit diagram.

Notes.

Assemble the circuit on a good quality PCB.

T1 can be a 230V primary, 35V/3A secondary step down transformer.

If 3A Bridge is not available, make one using four 1N5003 diodes.

LM317 must be fitted with a heat sink.

R2 = 0.85 ohm is not a standard value. You can obtain it by combining a 6.2 ohm and 1 ohm resistors in parallel.

F1 can be a 2A fuse.

To setup the charging voltage, power ON the charger and hook up a voltmeter across the output terminals and adjust R4 to make the voltmeter read 28V. Now the charger is ready and you can connect the batteries.

This charger is specifically designed for two 12V/7AH/6 cell lead acid batteries in series OR a 24V/7AH/12 cell lead acid battery.

Comments

Hello Seetharaman,
I am looking for charging circuit for 2nos of 4V 0.5Ah lead acid batteries connected in series . could you please publich a circuit for the same or you can provide the basic details like the voltage and current required for the same

hi,I am trying to build a charger for a 24v(two,12v 100Ah batteries connected in series). Each 12v battery consists of 6 cells. I have been trying hard with various configurations and failed in getting a proper design. Kindly suggest me a circuit to build a charger of the above mentioned characteristics.

Sir,
i am having 12V 7Ah Exide SMF Battery i need charger for it so please suggest me how may amp Charger its require for better performance, and make me available for details for solar charger for same.

Thanks for the above circuit for charging 24V,7Ah lead-acid batteries.
You have suggested that for 48V, 7AH battery we have to make two of the above circuit.
My requirements is to charge 48V 7AH (4 nos of serially connected 12V,7AH )
batteries with charge and dry indication,in a single circuit. I hope you can help reg this.

Hi I am Manic new to the designing part …. I need to charge my lead acid battery in series of 24v…it this circuit is enough or still i need some more modification in it…but i need to use SMPS for input supply please give the regarding information

Two 12 volts batteries of similar type and conditions can be charged up to a maximum of 7 AH only. As per your requirement of 26 AH a power pack capable of maximum current limit of 7 amps (9 amps preferred) is required.

Hi joe Two 12 volts batteries of similar type and conditions can be charged up to a maximum of 7 AH only. As per your requirement of 26 AH a power pack capable of maximum current limit of 7 amps (9 amps preferred) is required.

Good day. Pls I need your urgent assistance in responding to these questions to enable me modify this circuit to do something else. (1) Pls analyze the function of the BC547 in the circuit (2) What is the output of the LM317 (3) what could be the effect on the charger if I use a bigger transformer that is used for welding machine? Pls your response is urgently needed. Thanks

For charge indication you can one more transistor across R2 similar to Q1 R! and connect the collector through 2.7 K ohms 1/4 resistance in series with an LED (may be green for charging)to bridge rectifier positive. But for battery discharged indication you have to use an opamp similar to 741 and with a zener you can use it as a comparator when battery terminal voltage falls below 10.8 volts to indicate through red led..

i have chosen 24v battery charger as my project . i would like you to give me a handsome description of it so that i can understand it well and present it more clinically . if u can tell me the working of each component
and the whole circuit it would be a great help for me . plz reply on my email cz i got my valuable marks on it..

hi I want to make a circuit for charging of 2*12volt 40Ah batteries I can I use this circuit.
please mention that what is the purpose of BC547 in this circuit.
I have checked this circuit in Proteus & if I remove BC547 circuit still works/
PLEASE send me a circuit having indication when batteries are fully charged.
please reply me as soon as possible. THANKING you very much in anticipation

I am looking to make an in-car charging system for an electric mobility scooter – it uses a 24v 10Ah battery. The charger that I have (for use indoors) charges at 28.5 volts 1.6 amps. I have two questions –

1) can I substitute a 12v step-up DC-DC converter for the transformer and bridge rectifier section of your circuit to give me the DC input to the regulator, and what output voltage would the converter be required to supply?

2) what if any of the components of the regulated charger section would need to be changed to provide the correct output current and voltage?

Hi Mr. Seetharaman:
I’m a big fan of your circuits,and I would like to ask about the possibility of modifying this circuit so we can control charging current (like a pot. instead of R2), also kindly to explain to me why should sealed lead acid charging voltage be 13.6 not 15 volts as it is the cycle voltage written on it, and why max current is 700 mah not 2 amps as written also.
Thanks a lot

Hi Najeeb 13.6v is for normal cycle use charge voltage limitation. for boost charge 15.2 volt can be used. For rapid charge you can use 30% of the capacity of Lead Acid Batteries as the max current limit with 13.6 volt(for a fully exhausted battery not for partially discharged battery)but for a over night charge it is better to limit it to 10% of the rated capacity of the battery to avoid heating of the battery which will reduce it cycle life..

Hi Seetharaman
thanks a lot for this information and prompt reply. this is the circuit i was looking for my 24v SLA 14 AH battery . i will change R2 to .5 ohms.
can i use 2n3904 transistor instead of BC547 ?

Hi.
I’ve constructed this charger for a set of 2x12V/2Ah batteries changing R2 to 0.47 ohm. I tried to insert a second BC547 as suggested (base of 2nd BC547 to base of 1st and emitter to the other emitter and collector to a led and a 2.7K resistor to C1 positive) to indicate full charge with no luck whatsoever!
Am I doing something wrong?

Hi Dey you can use if the transformer is good quality low loss type (may be a torroidal)if not the regulation will be poor, charging time will become longer and may not charge a flat battery
Hi Gangadhar you can but ensure the output voltage is adjusted to 14.2 volts without load with pot R4.

i read on( http://www.circuitstoday.com/) 24 v lead acid battery charger circuit .i found a mistake in circuit details description (para 2) D1 is used for rectifier and D2 is prevent reverse flow of current from battery.kindly let it correct.
Mahmood Alam (MSc Electronics) from karachi ,Pakistan

hi, i built this circuit and its working well ,on testing.
i have few queries.
1) i got a 40 volts 5 amp transformer , is this suitable for charging two 12 v sla batteries, can a high amp damage the batteries.

2) how much time will it require for the batteries to be fully charged.can the charging time be reduced.
thanks

”
As the charge indicator is mandatory you can connect Q2 BC547 similar to Q1 with collector connected through an LED and a 2.7K ohm 1/4 Watt resistance to C1 positive. When the drop across R2 is greater than 0.65volt the LED will start glowing.”
Q2 collector connect to C1 ok. Where are connect to Q2 B and E?

It would appear that the circuit requested by P. R. Srinivas is exactly what I need for a charger for the battery pack for an APC Smart UPS 1500 — two 12v 18Ah sealed lead acid batteries connected in series. Would you please either post the modified circuit diagram or send the diagram and parts listing to my e-mail address which I have sent to you separately?

Hello Sir, I’m having a BLDC motor now(speci:0.25hp,24vdc,3000rpm).gng to do a project on EV with that motor.First part of it is to design a battery charger..pls guide me what type of battery will be good and also suggest me some circuit to design a good charger for it.. if u mail me I’ll be more thankful to u.. if any details is missing please mail me or post here.. Please help.. my mail id is:vishnukarthick108@gmail.com

Hello Sir, I’m having a BLDC motor now(speci:0.25hp,24vdc,3000rpm).gng to do a project on EV with that motor.First part of it is to design a battery charger..pls guide me what type of battery will be good and also suggest me some circuit to design a good charger for it.. if u mail me I’ll be more thankful to u.. if any details is missing please mail me or post here.. Please help.. my mail id is: vishnukarthick108@gmail.com

Hi CJ you are correct, Mr SOD requires 5 units to be charged that is 5 X 7.2 volts that is 36volts. Drop across LM338n is 5 volt drop across diode in the output circuit is 0.7. hence DC requirement at LM338 input is 41.7 volt at rated load current. Hence a 30Volt RMS at rated load is sufficient.

Hi Issac for 12 volt LA battery the maximum allowed terminal voltage is 14.2 , and the maximum initial current is 25% of the rated capacity. design a constant voltage charger with 14.2 volt regulated supply capable of supplying a maximum current limit of 25Amps. Supply this through a relay contact the relay should be an under voltage relay to open at 10.8 volts. the relay can be 12 volt @ 50 to 100mA coil with a contact rating of 30Amps DC. The UV switching circuit can be with a comparator
IC 741 with a transistor to switch the relay you can use any comparator circuit appeared earlier in Circuitstoday.

I built an inverter of 500w capacity that is using 12VDC/100AH Battery, but Iam faced with the problem of battery overdrain/overcharging. Pls, help me with a battery protection circuit that can disconnect a system at 10.8 and 15.0VDC. Thanks.

Hi Ocsee 10 batteries in series and 1.5AH each. Since you have already regulated 140DC it is just 1 volt higher than the required voltage. only current limiting is required. When battery is discharged fully terminal voltage will be around 10.8, that is 108 volts 140-108 @400mA 32 / 0.4 80 ohms 20 watt resistance is required. or you can use a MOSFET series current limiter for 400mA. Thyristor or triac cannot be used as you have already regulated 140Volt DC.

Just wondering if anyone has a charge with dump load circuit for my 24v system.I’m running 2 sets of 8v 4 cell lead acid 170ah batteries linked 3 in series then parralell.Just built an alternator from Fisher&Paykel motor,split the windings into 2 sections for vawt low speed winds.It puts out up to 100v rectified @ 2000rpm 40v @ 100rpm(unsure what amperage).Any help would be greatly apreciated.

Hi Kushlendr first reduce the transformer sec voltage to 15volt RMS AC. without connecting the output to battery set the output voltage to 13.8volts with R4 pot. reduce R5 to 0.5 ohms 2 watts connect to battery and charge it for 12 hrs.

Hi Stefan for charging 430AH 30V lead acid battery. you require a constant voltage source of 34.5 volts and maximum charging current limited to 30%, that is 130Amps. For boost charging 35.5 volt again limited to 100Amps. This requirement cannot be fulfilled by the above circuit.

gday there everybody was just looking at this circuit and i need to build a charger to charge a 430ah 30volt lead acid battery ,can anybody tell me if this circuit could be adapted to do so and what i would need to change .
thanks

Hi Srinivas sorry for the delay in replying. Change to LM338, transformer to 35 volt 5 amps. Bridge rectifier 7 amps or 6A4 X 4 for the bridge, reduce R5 to 0.125 ohms that is use 4nos 0.5 ohms 5 watts in parallel, Chenge D2 to 6A4 and fuse to 5 amps. since the current pulled by Q1 still low even with 120 ohms for R3 and 5 K for pot, BC547 can be still used 100 ohms is to limit base current during short circuit of the out put leads, i prefer a 470 ohms or 1K so that the base current is limitted to less than 20mA during just a short circuit. you can go ahead. you can send your further queations to my email id seethasub@hotmail.com

Hi every body,
I want to make a charger for 02 nos 12v lead acid batteries in series with each rating of 200AHs. Can any body help me to give a circuit. BAttery are for diesel genset and charger required for standby chargig. Please with detail..

Dear Mr. Seetharamanan,
” Greetings from FSMS Pvt. Ltd., Chennai “.
Thank you for the Charger Circuit (shown below) and explanations given. We would like to make a Charger to charge two 12V, 17Ah Lead Acid batteries connected in series.
I think that,
 The Transformer 35V/3A to be replaced with “Transformer 35V/5A”.
 The 3A bridge rectifier to replaced with “7A bridge”.
 Regulator LM317 to be replaced by “LM388”.
 BC547(Q1) to be replaced by “2N2955 power transistor”.
 100Ω (R1) to be replaced by “6.8 Ω”.
 0.85Ω/2W (R2) to be replaced by “0.1 Ω/5W”.

We would request you to provide me the Circuit for “Charger to charge two 12V, 17Ah Lead Acid batteries connected in series (24V, 17Ah)” (with explanation), with features of
o Automatic shutting down of charging voltage, when Battery charge is full, and vice versa.
o Charging indicator, charge-full indicator.
Awaiting for your earliest response.

Dear Mr.Seetharaman,
This circuit is really nice and i would request if you could send me a circuit diagram showing a RED LED while charging and a green LED when the battery is full. Rest everythng is ok with me.
Thanks in advance.
Cheers/Sathish

Hi Preeti Batteries cannot be charged in parallel as their present charecter will be different so better to charge the lead acid batteries in series. to charge them in parallel you require individual charging circuit for each battery from the charger

hello, i want to charge 6 lead acid batteries( each 12v/1.3 amp hour ). what will be the current requirement of the charging circuit? please help me if suitable circuit for charging batteries in parallel configuration is available.

Hi Anthony to charge sealed lead acid battery you should have aregulated power supply with 13.6 volts out put and the maximum initial charge current shoild not be greater than 30% of the rated capacity of the battery.

Thanx Seetharaman, next Q. If I go for 2N2955 option, how will the circuit change – can you send me a new diagram? I have read about charging SLA batteries, will this constant current charger decrease the life of SLA batteries-alternatively do you have a circuit to charge 24V 17Ah sealed lead acid battery?

Hi Anthony your idea correct, you have to change the transformer to 5 amp rating with the same voltage ofcourse a 7amp bridge LM388 or same 317 with 2N2955 (PNP power transistor with 6.8 ohms) to increase the current rating. 0.1 ohm 5 watts will do.(0.5 / 0.47 ohms 1 watt 5nos in parellel will also suit)

Hi Seetharaman, If I want to step up to enable me to charge 2x 12V 17Ah batteries in series can I use the same circuit as the 2x13Ah or would I have to change the following:
T1 30-35V 5A transformer, 7A Bridge rectifier, IC LM337 (?)- would I need to go for a 5A Voltage regulator and as I only know of Positive 3 terminal like LM338 I would need to change circuit? Lastly R2 to 0.1 ohm 10W . Alternatively step down to LM317 to drive 2N3055 transistors ?

Hi Seetharaman, This is a great circuit and near perfect for me, thanks.. I read your reply to Farada about switching on and off, but I cant figure out how to do this with your explanation. Is it possible you can draw this for me. I would like to be able to identify when batterys are charged and when they are charging (ie: with 2 LEDs?). So it will switch off and on sutomatically because my charger will be always connected. Also(!) can you protect from draining batterys if charger is switched off?
Thank you, Carl

Hi DYK this charger cannot used for charging 100 amp batteries. This can be used upto maximum capacity of 20AH.
batteries.
Hi Estephane can you give you battery’s complete detail and whether you want to charge them together or one at a time.

I desire to construct the circuit for an inverter in which can use two car batteries by which one battery to provides the dc input to the inverter and the second battery to be charged at the same time and vice versa without the need of solar power.Please can provide me with a circuit diagram?
Thank you in advance.

Hi for 24 volt 13AH lead acid gel battery the initial charging current (for a flat battery)preferrably sholud be limitted 3.5Amps max. With a regulated power supply of 27.6Volt. can charged for 12hrs to 15hrs max. As the battery terminal voltage increases tofinal level the charging will fall down slowly to trickle level. Hence the resistance value for R2 should be reduced to 0.2 ohms 5watts. Transformer rated at 30 volt 4amps bridge rectifier rated for 5amps and IC as LM337K (T03 casing)

Hi D2 is 1N5403. The transformer can be 30 volt AC at 1 Amp as our out put current is limited to less than 1 amp by Q1. As the charge indicator is mandatory you can connect Q2 BC547 similar to Q1 with collector connected through an LED and a 2.7K ohm 1/4 Watt resistance to C1 positive. When the drop across R2 is greater than 0.65volt the LED will start glowing.

i have a inverter circuit , but for charging we are using relay and capacitor.so the battery not charge fully, i heard abourt the circuit by using bta 12 triac and lm324 no need of relay and capacitor,can you help me

my requirement is instad of relay i need bta12 for switching for current limitting avoid capacitor

Hi, I have tried the circuit for charging the battery. But the charging current is too low. It reads only 70 milliAmps. I tried several times by adjusting the components but couldn’t get higher current. Does current varies on changing R2? How current varies with R2? How to get higher output current from the circuit. Please reply>

Hi, I have tried the circuit for charging the battery. But the charging current is too low. It reads only 70 milliAmps. I tried several times by adjusting the components but couldn’t get higher current. Does current varies on changing R2? How current varies with R2? How to get higher output current from the circuit. Please reply.